Java Message Service - What and Why? Bill Kelly, Silvano Maffeis SoftWired AG, Zürich

Agenda Make or Buy? Middleware Taxonomy, Messaging Java Message Service –Overview –Features of note –Its place in J2EE, EJB –Products For Further Information

Middleware - Make or Buy? Information systems are increasingly based on distributed architectures. Mobile and other new devices must be integrated: Server, PC, Laptop, PDA, Cell Phone,... New transport protocols (e.g. wireless), different qualities of service (best-effort, guaranteed,...). Systems become more complex, deadlines shorter. “Write-it-yourself” less an option.

Middleware Taxonomy Client/Server –a.k.a. RPC; procedure-oriented Distributed Objects –Object-oriented. CORBA, DCOM, RMI Message Oriented Middleware (MOM, Messaging) –“Connectionless”, “asynchronous” –Best known through message queuing

Messaging Messaging is a model in which applications are loosely coupled through the exchange of self- describing messages. Message Oriented Middleware (MOM) encompasses publish/subscribe and message queuing communications. Sender Receiver MOM Messages

Message Queuing ProducerQueueConsumer send(m1) send(m3) send(m2) receive() m1 m2 receive() Put message into queue Consume message

Publish/Subscribe Producer Broker Consumer publish(m1) send(m1) Pass message to broker send(m1) send(m2) Dispatch message to all consumers publish(m2) publish(m3)

Message Queuing Application

Publish/Subscribe Application subscribe (“AAPL”); subscribe (“SUN”); subscribe (“AAPL”); subscribe (“SUN”); publish (“AAPL”, 29.2); publish(“AAPL”, 29.3); publish (“SUN”, 43.0); publish(“SUN”, 42.7);

JMS Overview Goals of Java Message Service (JMS): Standardized API for Messaging in Java System-independent API for development of heterogeneous, distributed applications Use of arbitrary Java objects as messages Natural fit with XML messages (Extensible Markup Language) through data-centric model. Dual API for the two models: –Point to point (Message Queuing) –Publish-Subscribe

JMS Functionality Message Formats –TextMessage, BytesMessage, MapMessage (Hashtable), StreamMessage, ObjectMessage Quality of Service –Persistent/non-persistent delivery –Priorities, time to live, transactions Threaded programming model Outside the spec: –Security services –Management services

JMS Publisher Example Initialize JMS: session= connection.createTopicSession( transacted, ackMode); topic = session.createTopic(”quotes"); publisher= session.createPublisher(topic); Create a message: message= session.createTextMessage(…); Send a message: publisher.publish(message);

JMS Subscriber Example Initialize JMS: session= connection.createTopicSession(...); topic = session.createTopic(”quotes"); subscriber= session.createSubscriber(topic); Create a consumer: consumer= new MyConsumer(); subscriber.setMessageListener(consumer); Consumer receives messages via listener: void onMessage(Message message);

JMS Pub-Sub Classes

More JMS Features Message selectors: –SQL-like syntax for accessing header: subscriber = session.createSubscriber( topic, “priority > 6 AND type = ‘alert’ ”); –Point to point: selector determines single recipient –Pub-sub: acts as filter Transactions –void onMessage(Message m) { try { Message m2=processOrder(m); publisher.publish(m2); session.commit(); } catch(Exception e) { session.rollback(); }

Request/Reply with Messages “80% of inter-application communication is asynchronous, 20% is synchronous (RPC)” JMS also provides request/reply Request message includes Topic/Queue to reply to TopicRequestor/QueueRequestor helper classes Idea can easily be extended, e.g. iBus has: –Request with timeout –Request with multiple replies Uses: –Fault tolerance (N equivalent replyers).

JMS and J2EE, EJB Enterprise JavaBeans JavaServer Pages Servlets Java Naming and Directory Interface (JNDI) Java Transaction API (JTA) CORBA JDBC data access... and JMS! The J2EE Family: RMI, CORBA, JMS RMI, CORBA, JMS

JMS and Enterprise Java Beans Application server provides EJB, freeing applications from details of threading, transactions, scalability, fault-tolerance. JMS plays similar role to CORBA and RMI: connection from the outside wanting service. Full integration into EJB spec expected June App server transactions replace/augment JMS transactions. Messaging implementations from app-server vendors may not be as scalable, flexible as from “pure messaging vendors”.

JMS Products Pure Java –SoftWired iBus ( –Progress SonicMQ ( –FioranoMQ ( Java API, C/C++ Implementation –Sun’s JMQ Product JMS API to existing MOM Products –IBM MQSeries ( ibm.com/mqseries) Application Server Add-On –BEA Systems WebLogic, Borland Application Server.

Distinguishing Features of Products Pure Java? Pub-sub and point to point domains? Performance? Integration with other products, other languages? Quality of service and transport protocols (HTTP)? Security? XML? (usually simplistic) Management tools? Pricing, professional services, and support?

For Further Information Developing Java Enterprise Applications by Stephen Asbury and Scott R. Weiner. Wiley & Sons. has 80 pages on JMS, also addresses JNDI, EJB (OK overview book). SoftWired JMS articles: